Blocking oscillator



`Fume 7, 1955 B. DAMMERS ETAL 2,710,353

BLOCKING OSCILLATOR Filed Feb. 18, 1950 if l. :2U-max E BERNHARDUSsam-Anous DAMMERS ABRAHAM SEERTRUDA WILHELMUS UITJ'ENS IN V EN TOR52,710,353 Patented June 7, 1955 BLOCKING OSCILLATOR liernhardusGerhardus Dammers and Abraham Geertruda Wilhelmus Uitjens, Eindhoven,Netherlands, assignors to Hartford National Bank and Trust Company,Hartford, Conn., trustee Application February 18, 1950, Serial No.144,944

3 Claims. (Cl. Z50-36) The present invention relates to acircuit-arrangement for producing a sawtooth current in a coil connectedto the secondary of a transformer, the primary of which is included inthe output circuit of a discharge tube, and more particularly to acircuit-arrangement for the production of sawtooth current wherein thevoltage occurring across the secondary of the transformer during thesweep portion of the sawtooth current is rectified and the rectifiedvoltage is made operative in the output circuit of the discharge tube.

In circuit-arrangements of this type it has hitherto been customary tosupply to the control grid of the discharge tube a sawtooth voltage, orat least a voltage which increases after the unblocking of the tubewhich unblocking occurs upon exceeding a given threshold Value.

Due to this a very high anode-current is produced in the tube and if thetube is a screen-grid tube, the screengrid dissipation is alsoexcessively high.

The principal object of the present invention is to provide acircuit-arrangement for the production of a sawtooth current wherein adifferent method of controlling the discharge tube is employed so thatmaximum anode current is reduced.

Another object of the invention is to provide a circuitarrangement forproducing sawtooth current, wherein screen-grid dissipation of thedischarge tube is reduced.

Still another object of the present invention is to provide acircuit-arrangement for the production of saw-tooth currents wherein thephysical size of the discharge tube may be minimized.

Further objects of the invention will appear from the followingdescription.

According to the invention, a substantially constant voltage unblockingthe tube, which voltage is periodically interrupted by pulse voltagescutting ol the tube, is supplied to the control grid of the dischargetube.

In order that the invention may be more clearly understood and readilycarried into effect, it will now be described more fully with referenceto the accompanying drawing in which:

Figure 1 represents one embodiment of a circuit-arrangement according tothe invention,

Figure 2 is a current diagram by means of which the operation of theinvention will be explained, and

Figure 3 is a curve showing variation of the controlgrid voltage as afunction of time.

Referring now to the drawing, and more particularly to Figure l, thereis shown the basic elements of the circuitarrangement according to theinvention for producing a saw-tooth current, comprising a pentode 1, theanode circuit of which includes a primary Z of a transformer 3. A coil 5wherein the sawtooth current is produced, and which may be, for example,the deection coil of a cathode-ray tube is connected to a part of asecondary 4 of transformer 3.

One end of the secondaryv 4 is connected to the positive terminal of adirect current supply (not shown) which supplies a voltage Vb. The otherend of secondary coil 4 is connected to the anode of a diode 6. Thecathode of diode 6 is connected both to the end of the winding 2 remotefrom the anode of pentode 1 and, through a condenser 7, to the cathodeof pentode 1.

When the tube 1 is made conductive, the primary 2 of the transformer istraversed by a sawtooth' current. During the sweep portion of thiscurrent, a voltage having the polarity indicated in the drawing isdeveloped across the winding 4, with the result that the diode 6 becomesconductive and the condenser 7 is charged. This condenser is charged toa voltage approximately equal to the sum of the voltages of the directcurrent supply Vb and the Voltage occurring across the winding 4 duringthe sweep portion of the sawtooth current, so as to form a source ofdirect current supply of considerably higher voltage.

If the control at a control grid 8 of the pentode is effected by meansof a sawtooth voltage by which the pentode is unblocked on exceeding agiven negative bias, the current curves shown in Fig. 2 occur as afunction of time.

The tube 1 is traversed by a current Ia as shown by the curve 9 of Fig.2. This current has a maximum value Ia (max). The sawtooth currenttraversing coil 5, shown in curve 15 of Fig. 2, Varies between theValues I1 and +12, the value 114-12 being equal to 2 Imax if Imaxrepresents the amplitude of the sawtooth current.

From Fig. l it appears that the voltage Es across the primary of thetransformer is determined by where n represents the transformation ratioof the transformer.

From Fig. 2 it follows that:

2 q=g2=efticiency of coil plus transformer From both expressions itfollows that:

Iafmax) X (Vb-Vu) =2ImaxXEsX LEM In order to make the left-hand memberof (l) as small as possible:

1. K should be as small as possible which means that le (max) shouldpractically not exceed I2,

2. The eiciency i7 should be made as high as possible by rendering coil5 and transformer 3 as free as possible of losses.

3. The transformation ratio should approach as closely as possible tounity. To this end the pentode 1 should be controlled in a definitemanner.

ince, in the circuit shown in Fig. 1, the two transformer windings areconnected in series through the diode 6, and because the average primaryand secondary currents should be equal to one another and because afurther relation exists between the ampere turns in the two windings inconnection with the sawtooth current supplied to coil 5, thetransformation ratio in should not be chosen arbitrarily.

From this condition We may deduct the relation a=Q=ratio of the areasshown in Fig. 2 2 in the current diagram and b =%=relative current losswhich occurs in 1 the condenser 7 shown in Fig. 1

Ix being the current leaking from condenser 7.

When it is desired that the transformation ratio should approach unity,a should be made as high as possible which means, as appears from Fig.2, that the pentode should be controlled in such manner that the averageanode current Ia approaches as closely as possible the maximum anodecurrent Ia (max).

This is ensured by supplying the control grid of the pentode with acontrol voltage varying with time as shown in Fig. 3.

During the sweep portion of the sawtooth current traversing coil 5 inFig. 1, a substantially constant unblocking voltage Vg is available atthe control grid 8,

which voltage may, for example, be equal to the cathode potential of thepentode. During the fly-back, the tube 1 is cut of by a pulse voltage.

If the circuit-arrangement shown in Fig. 1 does not self-oscilate butis, for example, controlled by a preceding blocking oscillator, thenegative voltage pulses appearing across the anode of the tube of theblocking oscillator may be supplied to the control grid of thepentode 1. The circuit-arrangement shown in Fig. 1 is self-oscillatory.To this end a positive feedback path is provided between a tapping 10 onthe secondary of the transformer 3 and the control grid 8 of thepentode 1. This feedback path comprises a blocking condenser 11 and aresistance 12, which is preferably a variable re- BIBIXEI where thefactor 1 K 1 -lb -la is determined by the method of controlling thepentode.

In the known method of control, the value of this factor isapproximately 0.8 to 0.9, Whereas the use of the circuit-arrangementaccording to the invention permits a value lower than 0.4 to beattained. Owing to this, a stronger sawtooth current can be obtainedwith a materially lower pentode load.

VJhile we have described our invention in a speciiic use thereof and ina specic embodiment, we do not wish to be limited thereto, for obviousmodifications will occur to those skilled in the art Without departingfrom the spirit and scope of the invention.

We claim:

1. A circuit-arrangement for generating a sawtooth current, comprisingan electron discharge tube having a cathode, a control grid and ananode, an input circuit intercoupling said cathode and said controlgrid, an output circuit intercoupling said cathode and said anode, atransformer having a primary and a secondary Winding, said primarywinding being included in said output circuit, means to apply a positivepotential to one end of said secondary winding, an output coil coupledin parallel with a portion of said secondary winding, means to apply asubstantially constant potential to said input circuit to render saidtube conductive thereby producing a voltage in said secondary Windingand a current ow in said output coil, a capacitive element interposed insaid output circuit between said primary coil and said cathode, arectiher element coupled to the other end of said secondary winding andto said output circuit between said primary Winding and said capacitiveelement to rectify said voltage, and apply the rectiiied voltage to saidoutput circuit, and means to apply a pulse voltage to said input circuitperiodically to render said tube nonconductive thereby to arrest currentflow in said output coil.

2. A circuit arrangement, as set forth in claim l, wherein said means toapply a pulse voltage to said input circuit is constituted by feedbackmeans intercoupling said secondary Winding to said input circuit.

3. A circuit arrangement, as set forth in claim 2, Wherein said feedbackmeans includes a condenser connected in series with a resistor between apoint in said secondary winding and said grid.

References Cited in the le of this patent UNITED STATES PATENTS2,165,815 Rhea July 1l, 1939 2,250,686 Urtel July 29, 1941 2,512,543Haantjes et al. June 20, 1950

